An object of the present invention is to provide a device for eliminating lack of coating uniformity on the edges of electroplated metal strip. In particular, the invention is designed for continuous electroplating plants, where it can automatically remove any eventual coating irregularities on the edges of the strip.
There is a particular problem in the continuous plating of metal strip with other protective metals (such as zinc, or alloys of zinc with other metals such as iron or nickel, in the case of steel) by means of electrolytic processes, namely the point effect. This concentration of electrical charges in zones characterized by marked curvature results in the deposit there having a particular morphology and a typical acicular appearance connected with uncontrolled crystal growth. This leads to problems in the plant, since deposits of such acicular products may form on the current-carrying rolls--with obvious consequences for the rolls themselves--and on the strip, as well as in subsequent stages of operations. Thus, for instance, when pressing car-body elements, the breakaway of these crystals may cause marks on the press-formed part and even damage the dies in the long run.
Attempts to eliminate these undesirable products have already been made, for instance, by trimming the edges of the strip at the end of the plating line. However, this method calls for voluminous cutting equipment which is costly and space-consuming. It also eliminates corrosion protection on the edges of the trimmed strip, which creates a further problem. Attempts have been made to use tools located after each plating unit in contact with the edges of the strip and controlled by counterweight systems. In this case the problem is the need to ensure the continuous positioning of the cutters against the strip edge for each of the cleaning devices used. The present invention overcomes these difficulties by providing a device which automatically ensures uniform cleaning of the edges, in all the various configurations which result from changes in width and thickness.
According to the present invention, in a plant for the production of continuously electroplated metal strip, a device is installed which is characterized by the combination of:
means for detecting the presence of a joint between strips; PA1 means for detecting changes in strip width; PA1 a variety of tools for cleaning the strip edges; PA1 means for moving said variety of tools away from or towards the strip edges; PA1 means for detecting the positions of the strip edges; and PA1 means for optimizing tool position, pressure and contact angel vis-a-vis the strip.
After at least one electroplating unit and preferably at the end of the electroplating plant, the following items are arranged in succession in the direction of travel of the strip: a first set of sensors, optical for instance (such as photosensitive cells or image monitoring and processing systems) which detect the presence of a joint between strips, and a second set of sensors, also preferably optical, which provide information on changes in strip width (narrow to side or vice-versa).
In response to the signals sent by the sensors to the actuators, for instance of the electro-hydraulic or electro-pneumatic type, the latter can move the tools rapidly at right angles to the direction of travel of the strip, for instance, to ensure that the tools themselves, carried on special carriages, are not damaged as the result of a sudden shift in the position of the strip edge. In a successive zone there are other sensors, optical for example, whose task it is to guide the movement of the tools towards the operating positions on the edges of the strip, through the same actuators as above. Finally sensors, for example, of the inductive type, optimize tool position, pressure and contact angle vis-a-vis edges of the strip.